In such a turbomachine, the blades are immersed in a stream of gas that flows at speeds that are sometimes high, e.g. at supersonic speeds. The temperatures to which the blades are subjected vary widely, and for aviation turbomachines typically over the range −50° C. to more than 1000° C. The blades are therefore subjected to pressure forces and to temperature gradients that are considerable.
Because of the high temperatures and the associated temperature gradients, considerable stresses appear within the blades. These stresses can lead to cracks appearing, in particular cracks localized in the trailing edges of the blades. Such cracks naturally require the blades to be replaced.
In order to enable the blades to have the strength to withstand these stresses, it is known to provide ribs in the vicinity of their trailing edges. These ribs serve to stiffen the trailing edge but without that leading to excessive extra thickness that would reduce the aerodynamic performance of the blade. In general, the ribs all terminate at substantially the same distance from the trailing edge.
With reference to FIG. 2, an example blade has ribs in the vicinity of its trailing edge organized in a known manner that is described below. FIG. 2 is a diagram showing the airfoil 140 of a blade 110. This blade has ribs 150 disposed along its trailing edge 142. These ribs 150 occupy positions extending from the platform 130 all the way to the opposite ends 131 of the airfoil 140. They are substantially parallel to the top face 132 of the platform, i.e. its face that faces towards the airfoil. The ends 153 of the ribs 150 situated in the vicinity of the trailing edge are all situated at the same distance A therefrom. Furthermore, the opposite ends 155 of the ribs situated remotely from the trailing edge, together with the step 158 formed between the main surface 156 of the pressure side and the surface 154 of the trailing edge are situated at a distance B from the trailing edge 142 that is constant or substantially constant.
Nevertheless, it is found that such ribs are not effective in stabilizing the position of the trailing edge of the blade; in operation harmful deformation of the blade is observed, in particular in the vicinity of the trailing edge and in the curved connection fillet between the blade and the platform. The temperature gradient that exists between the pressure-side and the suction-side walls of the blade gives rise to non-linear movements in a direction that is substantially perpendicular to the trailing edge.
Furthermore, in spite of the ribs, the trailing edge of the blade continues to be a zone of weakness of the blade, where cracks can appear because of the very high thermomechanical stresses that occur therein operation. Such cracks lead naturally to the blade failing more or less rapidly. Because of this potential for the appearance of faults, the trailing edge is thus found to be a factor that limits the average lifetime of blades.